The invention relates to a method for cleaning and checking a particle filter of a motor vehicle, wherein in a first step soot particles which have collected in the particle filter are burnt. The invention further relates to a cleaning device for a particle filter.
German patent document DE 103 21 290 A1 describes a method for cleaning a particle filter of a motor vehicle, wherein soot particles that have collected in the particle filter are burnt in a soot burn-off process. In a flushing process after the soot burn-off process ash particles that have collected in the particle filter are removed from the particle filter by means of a flushing medium passed through the particle filter. During the soot burn-off process an oxygen concentration in a hot air flow, to which the particle filter is subjected, is set to less than 10%. When this concentration is exceeded the soot burn-off process is halted in order to avoid uncontrollable soot burn-off with inadmissibly high temperatures and to avoid thermal damage to the particle filter.
Exemplary embodiments of the present invention are directed to a method and a cleaning device that achieves improved cleaning of a particle filter.
In the inventive method, following the first step of burn-off of the soot particles, ash found in the particle filter is blower out by means of compressed a in a second step. Such a blowing-out by means of compressed air has proved to be particularly effective if it is a question of freeing the particle filter from ash, in particular ash of a low density with a slight load. An improved cleaning of the particle filter can thus be achieved. In addition the invention includes in relation to the cleaning process preliminary, intermediate and subsequent checks in order to facilitate quantifiable evidence of the cleaning efficiency.
An end face of the particle filter is hereby preferably subjected to a compressed air jet that covers less than 10% of a surface of the end face, wherein the compressed air jet is moved relative to the end face of the particle filter over the end face. Respective regions of the end face can thereby be subjected in a particularly good and targeted manner to the compressed air and the ash is thus removed from the particle filter. A particularly good cleaning result can be achieved if the compressed air jet covers less than 4% of the surface of the end face, is thus particularly greatly focused. It is thereby further advantageous if the whole end face is moved over spirally by the compressed air jet.
An outlet-side end face of the particle filter is preferably subjected to the compressed air jet, the ash is thus blown out in the counter current in relation to the direction in which during exhaust gas purification the exhaust gas usually flows through the particle filter. The ash can thus be removed particularly extensively from the particle filter.
It has been shown to be further advantageous if success of the cleaning is determined by measuring a dynamic pressure of a particle filter through which air flows respectively before the burn-off of the soot and after blowing out the ash. A dynamic pressure determination can additionally take place after the burn-off of the soot and before blowing out the ash. Through such a comparative measurement it is particularly simple to draw conclusions concerning the success of the cleaning and the state of the filter.
The respective dynamic pressure can hereby be measured while the particle filter is subjected to a defined, constant air mass flow, in particular at a constant temperature. A simple dynamic pressure measurement is thus sufficient in order to assess the success of the cleaning and the state of the filter. In addition or alternatively a detection of the change in the flow resistance of the particle filter can take place through dynamic pressure measurement in a different manner.
The particle filter is hereby initially subjected to a first air mass flow of a first, in particular constant, magnitude and a first pressure is hereby measured. Subsequently the particle filter is subjected to a second air mass flow of a second, in particular constant, magnitude and a second pressure is hereby measured. A pressure difference is formed from the first pressure and the second pressure. The success of the cleaning is then determined by comparing the respective pressure differences in the respective air mass flow before the cleaning process, thus before the burn-off of the soot, and after the cleaning process, thus after blowing out the ash or after an optionally carried out flushing stage with flushing liquid. The respective pressure differences are compared with each other in order to draw conclusions concerning the cleaning effect. This is favorable particularly as the behavior of the particle filter can be considered with different air mass flows particularly well in the determination of the cleaning performance. A detection of the flow resistance can of course also take place with constant pressure or dynamic pressure. In this connection the particle filter is initially subjected to a variable air mass flow until a defined dynamic pressure is reached. The success of the cleaning is then determined through comparative assessment of the respective air mass flows.
It has been shown to be further advantageous if, in dependence upon the cleaning success, the particle filter is subjected to a flushing liquid after blowing out the ash. The liquid cleaning hereby takes place advantageously only when the burn-off of the soot and the blowing out of the ash have not lead to the desired success of the cleaning. The process thereby requires particularly low resources. Such a flushing stage can be necessary in particular with a high ash load and/or in case of an ash load with a comparatively high density.
Even after subjecting the particle filter to the flushing liquid success of the cleaning can be determined by measuring a counter pressure. This can take place in the same way as before subjecting the particle filter to the flushing liquid or blowing out the ash.
In addition or alternatively after subjecting the particle filter to the flushing liquid a visual check of the particle filter can be carried out and the success of the cleaning can be determined with the aid of this visual check. Mechanical damage can also thereby optionally be recognized. For example, a side of the particle filter can be irradiated with light and the light passage through the particle filter on the other side thereof detected. Light of a certain wavelength, in particular infrared light, is thereby preferably used. The visual check thereby preferably covers the whole filter cross-section. If it is hereby determined that too great a proportion of the channels of the particle filter are still blocked, a new liquid cleaning can be carried out.
Finally, it has been shown to be advantageous if an underpressure is supplied to the particle filter during the blowing out of the ash. This suction of the ash can take place from the end face that lies opposite the end face subjected to the compressed air. By simultaneously subjecting to compressed air and supplying the underpressure the ash can be removed particularly effectively from the particle filter.
In the inventive cleaning device for a particle filter of a motor vehicle a heating device is provided that is designed to burn off soot particles that have collected in the particle filter. The cleaning device further comprises a compressed air unit, by means of which ash in the particle filter can be blown out of the particle filter.
The advantages and preferred embodiments described for the method according to the invention also apply to the cleaning device according to the invention.
The features and feature combinations mentioned above in the description and the features and feature combinations mentioned below in the description of the drawings and or shown only in the drawings can be used not only in the indicated combination but also in other combinations or alone without going outside of the scope of the invention.